Nitrogen oxides (NO.sub.x), are a significant pollutant generated during combustion and it is desirable to reduce their generation in carrying out combustion. Typically combustion is carried out by reacting fuel with air as the oxidant. As is known, nitrogen comprises nearly 80 percent of air and thus provides a large amount of nitrogen to the combustion reaction which may then react with oxygen to form NO.sub.x.
It is known that combustion may be carried with reduced NO.sub.x generation by using technically pure oxygen or oxygen-enriched air as the oxidant as this reduces the amount of nitrogen provided to the combustion reaction on an equivalent oxygen basis. However, using such an oxidant in place of air in a combustion reaction has two disadvantages. One disadvantage is the significantly increased costs of such oxidants relative to air. A second disadvantage is that the high oxygen concentration of such oxidants causes the combustion reaction to run at a higher temperature than would be the case if air were the oxidant. The higher temperature kinetically favors the formation of NO.sub.x thus counteracting the tendency to produce less NO.sub.x because less nitrogen is present.
Accordingly, it is an object of this invention to provide an improved combustion method wherein NO.sub.x generation is reduced while overcoming the disadvantages of the known NO.sub.x reduction combustion methods set forth above.